A prospective evaluation of zirconia anterior partial ﬁxed dental prostheses: Clinical results after seven years Maria Fernanda Solá-Ruíz, DMD, PhD, MD,a Rubén Agustin-Panadero, DMD, PhD,b Antonio Fons-Font, DMD, PhD, MD,c and Carlos Labaig-Rueda, DMD, PhD, MDd Since the end of the 20th ABSTRACT century, high-strength ceStatement of problem. Because of the high mechanical strength of zirconium dioxide, the metal in ramics have come into use to ﬁxed partial prostheses can now be replaced. However, the material is susceptible to aging or replace the metal in ﬁxed reshydrothermal degradation and to chipping of the feldspathic veneer. torations, a development that Purpose. The purpose of this prospective study was to evaluate the survival (without failure) and has led to high expectations.1 success (survival without any complication or failure) rate and clinical efﬁcacy of anterior zirconia Among the ceramics used in partial ﬁxed dental prostheses. these new systems, zirconium Material and methods. Twenty-seven anterior partial ﬁxed dental prostheses of 3 to 6 units were dioxide (zirconia) has been the fabricated. All participants were examined after 1 month and 6 months, then annually for 7 years. main focus of research because Results. Three partial ﬁxed dental prostheses failed and had to be removed: 2 because of secondary it offers a range of properties caries, which increased failure signiﬁcantly (P=.001) and 1 because of severe chipping. Six partial that make it suitable for use ﬁxed dental prostheses had complications: 2 debonded, 3 had chipping, and 1 had periapical in dentistry: biocompatibility, pathology. All veneer porcelain fractures occurred in 6-unit ﬁxed partial prostheses (P=.002). The high fracture resistance, low clinical success rate was 88.8% after the 7-year follow-up. thermal conductivity, resisConclusions. The clinical behavior of partial ﬁxed dental prostheses with a zirconium dioxide core tance to corrosion, and a in the anterior region provides an adequate medium-term survival rate. The main cause of failure totally crystalline microstrucwas secondary caries. The most frequent complication was chipping, which was directly related to ture.1,2 Yttrium-stabilized zirthe number of units of the prosthesis. (J Prosthet Dent 2015;-:---) conium dioxide is suitable for optical applications because of its high refraction index, inherent problem of the material is a phenomenon its low absorption coefﬁcient, and its high opacity in the known as spontaneous aging, hydrothermal degradation, visible and infrared spectra.3 Its grain size and the disor low-temperature degradation.6,7 These factors change tribution of different grain sizes, the pressure method its crystalline phase from tetragonal to monoclinic, which and conditions, and different additives all determine the increases the volume (4% to 5%) of the crystals causing translucency of a restoration.3 In spite of the material’s the loss of their mechanical properties and the appearhigh fracture resistance, chipping of the feldspathic porance of microcracks or macrocracks.6-9 celain veneer of zirconia ﬁxed dental prostheses during In spite of these setbacks, the survival rates of zirconia mastication is a frequent problem.4 This complication feldspathic ﬁxed partial dental prostheses (FDPs) are generates some uncertainty as to the long-term perforgreater than those of lithium disilicate-based core cemance of the material in dental restorations.5 An ramics10 and similar to those of metal ceramic prostheses,
Adjunct lecturer, Department of Buccofacial Prosthetics, Faculty of Medicine and Dentistry, University of Valencia, Valencia, Spain. Associate lecturer, Department of Buccofacial Prosthetics, Faculty of Medicine and Dentistry, University of Valencia, Valencia, Spain. c Senior lecturer, Department of Buccofacial Prosthetics, Faculty of Medicine and Dentistry, University of Valencia, Valencia, Spain. d Senior lecturer, Department of Buccofacial Prosthetics, Faculty of Medicine and Dentistry, University of Valencia, Valencia, Spain. b
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Clinical Implications Zirconia ﬁxed partial dental prostheses offer a recommendable alternative for replacing teeth in the esthetic zone.
which have survival rates of 97% and 99% after 5 years, respectively.11-14 Most published research has analyzed the behavior of zirconia restorations in the posterior zone.15,16 Chipping or delamination has been deﬁned as the fracture of the veneer ceramic, and a high rate varying between 6% and 28% has been conﬁrmed over a period of 3 to 10 years.1633 These are high values compared to the 4% fracture rate demonstrated by conventional metal ceramic restorations over 10 years.34 According to Heintze and Rousson,14 chipping, can be classiﬁed by severity and by the treatment required for repair, as follows: grade 1, small surface chipping, with treatment being polishing the restoration surface; grade 2, moderate surface chipping, with treatment being using a resin composite repair system (Fig. 1); and grade 3, severe veneer ceramic chipping exposing the zirconium dioxide core, with treatment being replacing the damaged prosthesis. Literature reviews such as those by Heintze and Rousson,14 Anusavice,35 and Raigrodski,36 show that the most frequent types of zirconia-based ﬁxed dental prostheses chipping are grades 1 and 2, which do not involve restoration failure. Several factors have been identiﬁed that can inﬂuence the incidence of chipping, as follows: (1) residual tension due to differences in the thermal expansion coefﬁcients of the core and the veneer materials; (2) poor wettability of the core by the veneer ceramic37; (3) compression resulting from ﬁring the porcelain38,39; (4) the protocol for heating and cooling the veneer and core37; (5) transformation of the zirconium dioxide crystal phase at the core-porcelain veneer interface caused by thermal inﬂuences or load forces40; (6) formation of inherent defects during processing41; (7) veneer ceramic application technique (stratiﬁcation/injection)41-43; (8) Inadequate thickness of veneer ceramic44; and (9) occlusal trauma.45 The aim of this study was to evaluate the success and survival rates and biological and/or mechanical complications of zirconium dioxide FDPs in the anterior region over a 7-year follow-up. MATERIAL AND METHODS Twenty-seven participants (14 women and 13 men) aged between 30 and 65 years took part in the study, which was carried out in the Prosthodontics and Occlusion Department at the University of Valencia between January 1, 2005, and January 1, 2006, with latest THE JOURNAL OF PROSTHETIC DENTISTRY
Figure 1. Chipping of veneer ceramic in maxillary central incisors of ﬁxed dental prosthesis with zirconia core.
evaluation being on January 1, 2014. The ethical board for clinical trials of the University of Valencia approved the study protocol, and all participants gave their informed consent to take part. Inclusion criteria were the need to replace 1 or 2 anterior teeth (central or lateral incisors), indicating the placement of FDPs of between 3 and 6 units, periodontally healthy abutment teeth, no signs of either resorption or periapical pathology, stable occlusion, and natural teeth in the antagonist arch. Individuals requiring a ﬁxed partial prosthesis of more than 2 pontics or with poor oral hygiene, a high incidence of caries, active periodontal disease, or bruxism were excluded. Prosthodontic procedures Three clinicians (S.R.M.F., A.P.R., F.F.A.) with experience in ﬁxed prosthodontics prepared the abutment teeth to meet the following parameters: occlusal and/or incisal reduction of 1.5 to 2 mm; axial reduction of 1 to 1.5 mm with a 10-degree included convergence angle, and a circular chamfer or shoulder of 1 mm. Particular attention was paid to rounded line angles (Figs. 2, 3). The color of each abutment tooth and adjacent teeth was identiﬁed with a shade guide (Vita shade guide, Vita Zahnfabrik). Interim restorations were fabricated from polymethyl methacrylate (AcryLux C&B; Ruthinium Group, Dental Manufacturing Spa) and cemented with eugenol-free interim cement (Temp Bond NE; Kerr Corp). Deﬁnitive impressions were made with polyvinyl siloxane impression material (Exaﬂex; GC America Inc) in a stock perforated stainless steel tray (Zhermack; Badia Polesine). Impressions of the opposing arch were made with irreversible hydrocolloid impression material (Orthoprint; Zhermack) and intermaxillary relations were registered in wax (X-hard; Miltex). The FDPs were fabricated with a computer-aided design and computer-aided manufacturing (CAD/CAM) Solá-Ruíz et al
Figure 2. Patient before treatment with existing ﬁxed dental prosthesis and tooth wear.
Figure 3. Abutment tooth preparation.
Figure 4. A, B, Zirconia framework evaluated intraorally to ensure adequate ﬁt.
system (Lava; 3M ESPE). They had a connector surface area of 7 mm2; a uniform coping thickness of 0.5 mm was used for all prostheses to standardize the study protocol. All internal frameworks were evaluated in the mouth to ensure an adequate ﬁt (Fig. 4). The veneer ceramic used was Lava Ceram (3M ESPE). Before bonding, the internal surfaces of the prosthetic framework were treated by airborne-particle abrasion with a tribochemical silica coating with 30 mm Al2O3 particles (CoJet; 3M ESPE). A layer of silane (Monobond; Ivoclar Vivadent) was applied. The teeth were also treated with 35% orthophosphoric acid, followed by application of the dentin adhesive (NT Prime Bond; 3M ESPE). All the FDPs were bonded with a resin cement (Multilink; Ivoclar Vivadent) (Fig. 5).
Figure 5. Fixed dental prosthesis cemented.
Clinical follow-up The 27 participants were examined by 2 clinicians who had not been involved in treating them, at 1 month after restoration, after 6 months, and thereafter annually for 7 years. The clinical parameters analyzed were loss of
vitality or infection of the abutment teeth (cold test and periapical radiographs), secondary caries, debonding, fracture of the prosthesis core, and chipping of the veneer ceramic. Both clinicians evaluated the prostheses independently. The parameters were such that assessment
Solá-Ruíz et al
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Figure 6. A, Incisal edge chipping level 1. Maxillary right canine. B, Chipping corrected with intraoral polishing.
Table 1. Complication details in prospective evaluation after 7 years Chipping Core fracture Debonding Secondary caries Endodontic
0.6 0.4 0.2
Survival Function 0
was objective in all prostheses, so reliability testing was not thought to be necessary. Nevertheless, if divergences did occur between their ﬁndings, the lower value was used for analysis. Statistical analysis was performed with software (Statistical Package for the Social Sciences; IBM SPSS Statistics) applying initial descriptive and bivariate analyses, the Kruskal-Wallis test, the Mann-Whitney test, and Kaplan-Meier survival analysis (a=.05). RESULTS The 27 participants received 27 FDPs: ten 3-unit, ten 4unit, two 5-unit, and ﬁve 6-unit FDPs. All participants completed the 7-year follow-up, and no appointments were missed. After 7 years of monitoring, 3 complete restoration failures had occurred requiring removal (one 3-unit and one 4-unit FDP failure because of secondary caries and one 6-unit FDP failure because of irreparable chipping). The survival rate of the zirconia core restorations was 88.8% after the 84-month follow-up (95% conﬁdence interval [CI] 70.8 to 97.7). The complications observed were classiﬁed as biological (secondary caries, pulp affectation) or mechanical (fracture of the core or veneer ceramic, debonding). Biological complications involved 2 FDPs (one 3 unit, one THE JOURNAL OF PROSTHETIC DENTISTRY
Complication time Figure 7. Probability of survival without complications until end of follow-up period.
4 unit) with secondary caries (7.4%) in the abutment teeth, requiring replacement of the prosthesis at the 3year follow-up and one 4-unit FDP (3.7%) with an endodontic problem with periapical lesions after 2.5 years; however, after periapical surgery, there was no need to replace the prosthesis. Mechanical complications involved 4 FDPs with chipping (14.8%), all of them 6unit FDPs: one was replaced after 3 years and the others were corrected by polishing and intraoral repair (Fig. 6). Two FDPs (one 4 unit and one 6 unit) debonded after 7 and 6 months, respectively. None of the FDPs had fracture of the internal zirconia cores (Table 1). When the type of complication was related to the FDP’s number of units (applying the Kruskal-Wallis test), a statistically signiﬁcant relation was identiﬁed involving chipping (P=.002). Five 6-unit FDPs showed a higher incidence of chipping than those with shorter spans (P